Distortion compensation table creation method and distortion compensation method

ABSTRACT

Fundamentals and IM waves comprising distortion signals are detected by vector measurement from an amplified baseband signal. Detected IM waves are related to power and frequency and plotted on the frequency axis. IM waves related to power and frequency are subjected to IFFT processing, and thereby converted so as to be related to time and power. Amplitude and phase components of IM waves subjected to IFFT processing are found. Compensation signal generation information is generated by relating a distortion compensation signal that has amplitude components of inverse amplitude to the amplitude components of IM waves and phase components of inverse phase to the phase components of IM waves to power, and creating a table by storing the generated compensation signal generation information in a compensation table. By this means, the circuit configuration can be made small and simple, processing can be simplified and speeded up, and distortion components can be suppressed with high precision.

TECHNICAL FIELD

The present invention relates to a distortion compensation tablecreation method and distortion compensation method, and, for example, toa distortion compensation table creation method and distortioncompensation method that eliminate distortion generated when a signal isamplified.

BACKGROUND ART

Heretofore a predistortion distortion compensation apparatus has beenknown as an apparatus that compensates for distortion generated when atransmit signal is amplified in a radio communication apparatus. FIG. 1is a block diagram showing the configuration of a conventionalpredistortion distortion compensation apparatus 100.

Conventional predistortion distortion compensation apparatus 100 iscomposed of a baseband I input terminal 101, a baseband Q input terminal102, a power calculation section 103, a compensation data table 104, acomplex multiplication section 105, a digital/analog converter(hereinafter referred to as “DAC”) 106, a DAC 107, a modulator(hereinafter referred to as “MOD”) 108, an oscillator 109, a poweramplifier 110, a directional coupler 111, an RF output terminal 112, ademodulator (hereinafter referred to as “DEMOD”) 113, an analog/digitalconverter (hereinafter referred to as “ADC”) 114, an ADC 115, acompensation data computation section 116, and a delay section 117.

In FIG. 1, a baseband I signal is input to baseband I input terminal 101and a baseband Q signal that is orthogonal data with respect to the Isignal is input to baseband Q input terminal 102, and these signals passthrough DAC 106 and DAC 107, and are modulated to RF signals by MOD 108.The signal modulated to RF then undergoes power amplification by poweramplifier 110 and is output from RF output terminal 112.

At this time, since power amplifier 110 performs nonlinear operation,distortion is generated in the signal amplified by power amplifier 110.A predistortion function is a function for amending the nonlinearity ofpower amplifier 110 to linearity. In order to perform power amplifier110 linearity compensation, compensation data table 104 is provided withcompensation data corresponding to power values. Power calculationsection 103 performs input baseband signal power calculation everysampling time and outputs the result to compensation data table 104.Compensation data table 104 is referenced using the power calculationresult input from power calculation section 103, and the necessarycompensation data is extracted and output to complex multiplicationsection 105. Complex multiplication section 105 operates so as tosuppress distortion generated in power amplifier 110 for the input Isignal and Q signal.

In order to perform accurate linearity compensation, accuracy ofcompensation data table 104 is required. Therefore, conventionally, apower amplifier 110 output signal is taken from directional coupler 111,processing is performed by compensation data computation section 116 tocalculate a distortion component of a signal demodulated by DEMOD 113corresponding to a baseband signal prior to amplification, and acompensation data table is created to compensate for the calculateddistortion component. By this means, an accurate compensation data tablecan be created.

However, a problem with a conventional distortion compensation tablecreation method and distortion compensation method is that DEMOD 113 andcompensation data computation section 116 are necessary for compensationdata table 104 generation, resulting in a large and complex circuitconfiguration. A further problem with a conventional distortioncompensation table creation method and distortion compensation method isthat, since it is necessary to perform demodulation processing in DEMOD113 and computational processing to find compensation data incompensation data computation section 116, processing is complex andcannot be executed at high speed.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a distortioncompensation table creation method and distortion compensation methodthat enable a small and simple circuit configuration to be used, enableprocessing to be simplified and speeded up, and also enable distortioncomponents to be suppressed with high precision.

This object can be achieved by finding a distortion component generatedwhen a baseband signal is amplified by relating frequency to basebandsignal power, converting the distortion component found by relatingfrequency to power so as to be related to time and power, and alsofinding an amplitude component and phase component in a distortioncomponent converted so as to be related to time and power for eachpower, and relating a distortion compensation signal that has a foundamplitude component of inverse amplitude to the amplitude component anda found phase component of inverse phase to the phase component topower, and performing storage in a table as compensation signalgeneration information for selecting a distortion compensation signalthat suppresses distortion components.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a conventionaldistortion compensation apparatus;

FIG. 2 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 1 of the present invention;

FIG. 3 is a flowchart showing a compensation data table creation methodaccording to Embodiment 1 of the present invention;

FIG. 4 is a drawing showing on the frequency axis a two-wave signalinput to an amplifier according to Embodiment 1 of the presentinvention;

FIG. 5 is a drawing showing on the frequency axis a signal output froman amplifier according to Embodiment 1 of the present invention;

FIG. 6 is a drawing showing on the time axis the power values of asignal output from an amplifier according to Embodiment 1 of the presentinvention;

FIG. 7 is a drawing showing by means of the relationship betweencompensation data power and amplitude the nonlinear characteristic of anamplifier according to Embodiment 1 of the present invention;

FIG. 8 is a drawing showing by means of the relationship betweencompensation data power and phase the nonlinear characteristic of anamplifier according to Embodiment 1 of the present invention;

FIG. 9 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 2 of the present invention;

FIG. 10 is a drawing showing on the frequency axis a signal output froman amplifier according to Embodiment 2 of the present invention;

FIG. 11 is a drawing showing on the time axis the power values of asignal output from an amplifier for creating a compensation data tableaccording to Embodiment 2 of the present invention;

FIG. 12 is a drawing showing by means of the relationship betweencompensation data power and amplitude the nonlinear characteristic of anamplifier according to Embodiment 2 of the present invention;

FIG. 13 is a drawing showing by means of the relationship betweencompensation data power and phase the nonlinear characteristic of anamplifier according to Embodiment 2 of the present invention;

FIG. 14 is a drawing showing by means of the relationship betweencompensation data power and amplitude the nonlinear characteristic of anamplifier according to Embodiment 2 of the present invention;

FIG. 15 is a drawing showing by means of the relationship betweencompensation data power and phase the nonlinear characteristic of anamplifier according to Embodiment 2 of the present invention;

FIG. 16 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 3 of the present invention;

FIG. 17 is a drawing showing the relationship between amplitude andpower when account is not taken of hysteresis of a signal output from anamplifier according to Embodiment 3 of the present invention;

FIG. 18 is a drawing showing the relationship between phase and powerwhen account is not taken of hysteresis of a signal output from anamplifier according to Embodiment 3 of the present invention;

FIG. 19 is a drawing showing the relationship between power andamplitude when account is taken of hysteresis of a signal output from anamplifier according to Embodiment 3 of the present invention;

FIG. 20 is a drawing showing the relationship between power and phasewhen account is taken of hysteresis of a signal output from an amplifieraccording to Embodiment 3 of the present invention;

FIG. 21 is a drawing showing the relationship between power andamplitude in a compensation signal according to Embodiment 3 of thepresent invention;

FIG. 22 is a drawing showing the relationship between power and phase ina compensation signal according to Embodiment 3 of the presentinvention;

FIG. 23 is a drawing showing the relationship between power andamplitude in a compensation signal according to Embodiment 3 of thepresent invention; and

FIG. 24 is a drawing showing the relationship between power and phase ina compensation signal according to Embodiment 3 of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the accompanying drawings, embodiments of thepresent invention will be explained in detail below.

Embodiment 1

FIG. 2 is a block diagram showing the configuration of a transmittingapparatus 200 according to Embodiment 1 of the present invention. InFIG. 2, transmitting apparatus 200 is mainly composed of an inputterminal 201, an input terminal 202, a power calculation section 203, acompensation data table 204, a complex multiplication section 205, a DAC206, a DAC 207, an oscillator 208, a MOD 209, an amplifier 210, and anantenna 211.

Input terminals 201 and 202, power calculation section 203, compensationdata table 204, complex multiplication section 205, DAC 206, DAC 207,oscillator 208, MOD 209, and amplifier 210 make up a distortioncompensation apparatus 212. For distortion compensation apparatus 212 inFIG. 2, a predistortion distortion compensation apparatus configurationis shown, with power calculation section 203, compensation data table204, and complex multiplication section 205 forming a predistortionfunction.

Input terminal 201 receives an I component baseband signal and sendsthis signal to power calculation section 203 and complex multiplicationsection 205.

Input terminal 202 receives a Q component baseband signal and sends thissignal to power calculation section 203 and complex multiplicationsection 205.

Power calculation section 203 performs power calculations for basebandsignals input from input terminal 201 and input terminal 202 everysampling time, and outputs measured power information, which iscalculated power information, to compensation data table 204.

Compensation data table 204 is a data table for performing linearcompensation of the amplifier, which has nonlinear characteristics, andholds vector value information. Compensation data table 204 outputs acompensation signal comprising compensation signal generationinformation, in which amplitude component and phase componentcompensation information selected using measured power information inputfrom power calculation section 203 is held as a vector value, to complexmultiplication section 205. The method of creating the compensationtable held by compensation data table 204 will be described laterherein.

Complex multiplication section 205 suppresses IM waves comprisingbaseband signal distortion components based on the baseband signalsinput from input terminal 201 and input terminal 202 and thecompensation signal input from compensation data table 204, and outputsthe resulting signals to DAC 206 and DAC 207.

DAC 206 converts the baseband signal input from complex multiplicationsection 205 from analog data to digital data, and outputs this digitaldata to MOD 209.

DAC 207 converts the baseband signal input from complex multiplicationsection 205 from analog data format to digital data format and generatesa digital converted signal, and outputs this signal to MOD 209.

Oscillator 208 is a local oscillator that outputs a predeterminedfrequency signal to MOD 209.

MOD 209 modulates digital converted signals input from DAC 206 and DAC207 using a signal input from oscillator 208 and generates a modulatedsignal, and outputs this modulated signal to amplifier 210.

Amplifier 210 amplifies the modulated signal input from MOD 209 andsends the amplified signal to antenna 211.

Next, the method of creating the compensation table held by compensationdata table 204 will be described using FIG. 3 through FIG. 8. Thecompensation table is created before a distortion component suppressionoperation.

First, as shown in FIG. 4, a two-wave signal comprising two waves (twotones), fundamental #401 and fundamental #402, is input to amplifier 210(step ST301) Next, the input two-wave signal is amplified by amplifier210, and the fundamentals and IM waves in the amplified two-wave signalundergo vector measurement by means of a vector signal analyzer (stepST302). By this means, the fundamentals and IM waves can be obtained asvector values on the frequency axis, and can be obtained not only aspower values (amplitude values) but also as phase values. Vectormeasurement can be carried out by any method, not only by using a vectorsignal analyzer.

Next, based on the measurement results, the fundamental phase differenceof the two-wave signal is corrected so that the fundamental phasedifference becomes 0 degrees, and IM wave phase correction is carriedout in accordance with the amount of fundamental phase correction (stepST303). Also, correction is performed so that the phase difference ofthe input two-wave signal becomes 0 degrees (step ST303).

Then, as shown in FIG. 5, fundamentals and IM waves reflecting thesecorrections are plotted as a frequency axis series (f-dat-out) (stepST304). By amplifying the input two-wave signal, IM waves #501, #502,#503, #504, #505, and #506 are generated in addition to fundamentals#507 and #508. IM waves #501, #502, #503, #504, #505, and #506 aregenerated as distortion components of fundamentals #507 and #508, andthe further these IM waves are from fundamentals #507 and #508 on thefrequency axis, the smaller is their power. Plotting is also performedas a frequency axis series (f-dat-in) for an input two-wave signalsubjected to phase correction (step ST304).

Next, IM waves #501, #502, #503, #504, #505, and #506 plotted asfrequency axis series (f-dat-out) are subjected to inverse fast Fouriertransform (hereinafter referred to as “IFFT”) processing, and convertedto a time axis series (t-dat-out) (step ST305). Also, the two-wavesignal plotted as a frequency axis series is subjected to IFFTprocessing and converted to a time axis series (t-dat-in) (step ST305).FIG. 6 shows an output signal #601 and input signal #602 converted to atime axis series as power values.

Then, using Equation (1) the amplifier 210 transfer function is obtainedfrom the obtained amplifier input signal and output signal frequencyaxis series (step ST306).AMP(t)=(t-dat-out)/(t-dat-in)   (1)where

AMP(t): Amplifier 210 transfer function

(t-dat-out): Time axis series

(t-dat-in): Frequency axis series

Amplifier transfer function AMP(t) expressed by a time function isconverted to input signal power function AMP(P) using Equation (2) (stepST307).P=abs(t-dat-in)   (2)where

P: Input signal power

abs(t-dat-in): Root-mean-square value

It is then determined whether or not the predetermined number ofmeasurements by means of the vector signal analyzer have finished (stepST308). If the predetermined number of measurements have finished, themeasurement results are combined and transfer function AMP(P) is found.

Here, the compensation table stored by compensation data table 204 isstored as vector information, and the vector information has bothamplitude and phase information. Therefore, compensation data table 204has amplitude and phase components corresponding to power P input toamplifier 210 as a compensation data table. That is to say, therelationship between an input signal to amplifier 210 and an outputsignal from amplifier 210 is expressed as shown in Equation (3).Output signal=AMP(P)×input signal   (3)where AMP(P): Amplifier 210 transfer function

Also, amplifier transfer function AMP(P) is expressed as shown inEquation (4).AMP(P)=A(P)×e ^(−jθ(P))   (4)where

P: Input power

A(P): Amplitude component

θ(P): Phase component

The meaning of nonlinearity taken to be a problem here is thatamplification characteristic A(P) and phase characteristic θ(P)fluctuate. Compensation to linearity means compensation to a fixed-poweramplifier 210 transfer function. Therefore, the compensation signal canbe expressed as a power P function as shown in Equation (5).Compensation signal (P)=AMP(fixed)/AMP(P)   (5)where

AMP(fixed): Fixed-power amplifier 210 transfer function

AMP(P): Amplifier 210 transfer function

Thus, amplifier 210 transfer function AMP(P) can be found using Equation(5).

Next, a transfer function is found that has an amplitude component ofinverse amplitude to the amplitude component in the amplifier 210transfer function found from Equation (5) and a phase component ofinverse phase to the phase component in the amplifier 210 transferfunction found from Equation (5) with respect to an amplitude componentand phase component when the amplifier 210 output signal has a linearcharacteristic, and the found transfer function is converted and storedas a compensation table (step ST309).

On the other hand, if the predetermined number of measurements have notfinished in step ST308, the processing from step ST301 through stepST307 is repeated until the predetermined number of measurements havefinished.

FIG. 7 is a drawing showing the relationship between compensation datapower and amplitude in the compensation table, and FIG. 8 is a drawingshowing the relationship between compensation data power and phase inthe compensation table. FIG. 7 shows a case where, with regard to therelationship #702 between amplitude and power, amplifier 210 haslinearity, and since amplifier 210 is actually nonlinear, it has thenonlinear characteristic of relationship #701 between amplitude andpower. Therefore, compensation data table 204 stores, as compensationdata, relationship #703 between amplitude and power symmetrical withrelationship #701 between amplitude and power that the actual signalafter amplitude has with respect to relationship #702 between anamplitude component and power when amplifier 210 has linearity. By thismeans, compensation data amplitude components become amplitudecomponents of inverse amplitude to the amplitude components in amplifier210 IM waves with respect to amplitude components when the amplifier 210output signal has a linear characteristic. Similarly, FIG. 8 shows acase where, with regard to the relationship #802 between phase andpower, amplifier 210 has linearity, and since amplifier 210 is actuallynonlinear, it has the nonlinear characteristic of relationship #801between phase and power. Therefore, compensation data table 204 stores,as compensation data, relationship #803 between amplitude and powersymmetrical with relationship #801 between amplitude and power that theactual signal after amplitude has with respect to relationship #802between amplitude and power when amplifier 210 has a linearcharacteristic. By this means, compensation data phase components becomephase components of inverse phase to the phase components in amplifier210 IM waves with respect to phase components when the amplifier 210output signal has a linear characteristic.

Next, a description will be given of the operation of transmittingapparatus 200 in a distortion component suppression operation thatsuppresses IM waves #501, #502, #503, #504, #505, and #506 shown in FIG.5.

A baseband signal is input to power calculation section 203 and complexmultiplication section 205 as orthogonal data composed of an I componentand a Q component. Power calculation section 203 calculates power fromthe input baseband signals. Then, in compensation data table 204,compensation data is referenced using measured power information and acompensation signal phase component is found, and also compensation datais referenced using measured power information and a compensation signalamplitude component is found. At this time, the relationship betweenamplitude and power stored by compensation data table 204 is that shownin FIG. 7, and the relationship between phase and power stored bycompensation data table 204 is that shown in FIG. 8. Then compensationdata table 204 finds a compensation signal using the phase components ofthe found phase and the amplitude components of the found amplitude, andoutputs this compensation signal to complex multiplication section 205.The compensation signal is found as a vector from the phase andamplitude components.

Then IM waves #501, #502, #503, #504, #505, and #506, which aredistortion components generated when the baseband signal is amplified byamplifier 210, are suppressed by combining the compensation signal andbaseband signal in complex multiplication section 205.

Thus, according to Embodiment 1, distortion components generated when abaseband signal is actually amplified are found as a frequency axisseries, and also the found frequency axis series is subjected to IFFTprocessing and converted to a time axis series, and a compensation tableof the time of compensation signal generation is created, so that bygenerating a distortion compensation signal based on distortioncomponents actually generated in a baseband signal, a compensationsignal that takes account of frequency characteristics can be generated,and distortion components can be suppressed with high precision. Also,according to Embodiment 1, demodulation processing and so forth isrendered unnecessary and the circuit configuration can be made small andsimple, and furthermore processing can be simplified and speeded up.

Embodiment 2

FIG. 9 is a block diagram showing the configuration of a transmittingapparatus 900 according to Embodiment 2 of the present invention.

As shown in FIG. 9, in transmitting apparatus 900 according toEmbodiment 2, as compared with transmitting apparatus 200 according toEmbodiment 1 shown in FIG. 2, a table switching section 903 is added,and a compensation data up table 901 and a compensation data down table902 are provided instead of compensation data table 204. Parts in FIG. 9identical to those in FIG. 2 are assigned the same codes as in FIG. 2,and descriptions thereof are omitted.

In FIG. 9, transmitting apparatus 900 is mainly composed of inputterminal 201, input terminal 202, power calculation section 203, complexmultiplication section 205, DAC 206, DAC 207, oscillator 208, MOD 209,amplifier 210, antenna 211, compensation data up table 901, compensationdata down table 902, and table switching section 903.

Input terminals 201 and 202, power calculation section 203, complexmultiplication section 205, DAC 206, DAC 207, oscillator 208, MOD 209,amplifier 210, compensation data up table 901, compensation data downtable 902, and table switching section 903 make up a distortioncompensation apparatus 904. For distortion compensation apparatus 904 inFIG. 9, a predistortion distortion compensation apparatus configurationis shown, with power calculation section 203, complex multiplicationsection 205, compensation data up table 901, compensation data downtable 902, and table switching section 903 forming a predistortionfunction.

Compensation data up table 901 is a data table for performing linearcompensation of the amplifier, which has nonlinear characteristics, andholds vector value information. Compensation data up table 901 outputs acompensation signal in which amplitude component and phase componentcompensation information (rising-time compensation signal generationinformation) selected by referencing compensation data using measuredpower information input from power calculation section 203 is held as avector value, to complex multiplication section 205.

Compensation data down table 902 is a data table for performing linearcompensation of the amplifier, which has nonlinear characteristics, andholds vector value information. Compensation data down table 902 outputsa compensation signal in which amplitude component and phase componentcompensation information (falling-time compensation signal generationinformation) selected by referencing compensation data using measuredpower information input from power calculation section 203 is held as avector value, to complex multiplication section 205.

Table switching section 903 determines from measured power informationfor different times input from power calculation section 203 whethermeasured power according to the latest measured power information hasrisen or fallen from past measured power. Then, if the latest measuredpower has risen from past measured power, table switching section 903outputs the compensation signal input from compensation data up table901 to complex multiplication section 205. On the other hand, if thelatest measured power has fallen from past measured power, tableswitching section 903 outputs the compensation signal input fromcompensation data down table 902 to complex multiplication section 205.

Next, the method of creating the compensation tables used incompensation data up table 901 and compensation data down table 902 willbe described using FIG. 10 through FIG. 15. The compensation tables arecreated before a distortion component suppression operation. As thecompensation table creation method flow chart is identical to that inFIG. 3, and the figure showing the pre-amplification baseband signal asa frequency series is identical to FIG. 4, FIG. 3 and FIG. 4 will beused in the following description.

First, as shown in FIG. 4, a two-wave signal comprising two waves,fundamental #401 and fundamental #402, is input to amplifier 210 (stepST301).

Next, the input two-wave signal is amplified by amplifier 210, and thefundamentals and IM waves in the amplified two-wave signal are measuredby means of a vector signal analyzer (step ST302). By this means, thefundamentals and IM waves can be obtained as vector values on thefrequency axis, and can be obtained not only as power values (amplitudevalues) but also as phase values. Vector measurement can be carried outby any method, not only by using a vector signal analyzer.

Next, based on the measurement results, the fundamental phase differenceof the two-wave signal is corrected so that the fundamental phasedifference becomes 0 degrees (step ST303). Also, correction is performedso that the phase difference of the input two-wave signal becomes 0degrees (step ST303).

Then, as shown in FIG. 10, IM waves reflecting these corrections areplotted as a frequency axis series (f-dat-out) (step ST304). Byamplifying the input two-wave signal, IM waves #1001, #1002, #1003, and#1004 are generated in addition to fundamentals #1005 and #1006. IMwaves #1001, #1002, #1003, and #1004 are generated as distortioncomponents of fundamentals #1005 and #1006, and the further these IMwaves are from fundamentals #1005 and #1006 on the frequency axis, thesmaller is their power. The power levels of IM wave #1002 and IM wave#1003 detected at symmetrical positions on the frequency axis withrespect to fundamentals #1005 and #1006 are different, and the powerlevels of IM wave #1001 and IM wave #1004 detected at symmetricalpositions on the frequency axis with respect to fundamentals #1005 and#1006 are different. Plotting is also performed as a frequency axisseries (f-dat-in) for an input two-wave signal subjected to phasecorrection (step ST304).

Next, IM waves#1001, #1002, #1003, and #1004 plotted as frequency axisseries (f-dat-out) are subjected to IFFT processing, and converted to atime axis series (t-dat-out) (step ST305). FIG. 11 shows an outputsignal and input signal converted to a time axis series as power values.As shown in FIG. 11, relationship #1102 between time and power in anactual amplifier 210 output signal is distorted with respect torelationship #1101 between time and power when a amplifier 210 outputsignal in which distortion has not occurred has undergone IFFTprocessing, due to the fact that the power of IM wave #1002 and thepower of IM wave #1003 differ and the power of IM wave #1001 and thepower of IM wave #1004 differ.

Then an amplifier 210 transfer function is obtained from the obtainedamplifier input signal and output signal frequency axis series usingEquation (1) (step ST306) Also, amplifier 210 transfer function AMP(t)expressed by a time function is converted to input signal power functionAMP(P) using Equation (2) (step ST307).

It is then determined whether or not the predetermined number ofmeasurements by means of the vector signal analyzer have finished (stepST308) If the predetermined number of measurements have finished, themeasurement results are combined and transfer function AMP(P) is foundusing Equation (5).

Next, a transfer function is found that has an amplitude component ofinverse amplitude to the amplitude component in the amplifier 210transfer function found from Equation (5) and a phase component ofinverse phase to the phase component in the amplifier 210 transferfunction found from Equation (5) with respect to an amplitude componentand phase component when the amplifier 210 output signal has a linearcharacteristic, and the found transfer function is converted and storedas a compensation table (step ST309). At this time, a compensation tableis stored separately for the case where amplifier 210 input power is onan upward trend and the case where amplifier 210 input power is on adownward trend.

On the other hand, if the predetermined number of measurements have notfinished in step ST308, the processing from step ST301 through stepST307 is repeated until the predetermined number of measurements havefinished.

FIG. 12 is a drawing showing the relationship between compensation datapower and amplitude in compensation data up table 901, FIG. 13 is adrawing showing the relationship between compensation data power andphase in compensation data up table 901, FIG. 14 is a drawing showingthe relationship between compensation data power and amplitude incompensation data down table 902, and FIG. 15 is a drawing showing therelationship between compensation data power and phase in compensationdata down table 902.

FIG. 12 shows a case where, with regard to relationship #1202 betweenamplitude and power, amplifier 210 has linearity, and since amplifier210 is actually nonlinear, it has the nonlinear characteristic ofrelationship #1201 between amplitude and power. Therefore, compensationdata up table 1001 stores, as compensation data, relationship #1203between amplitude and power symmetrical with relationship #1201 betweenamplitude and power that the actual signal after amplitude has withrespect to relationship #1002 between amplitude and power when amplifier210 has linearity.

Similarly, FIG. 13 shows a case where, with regard to relationship #1302between phase and power, amplifier 210 has linearity, and sinceamplifier 210 is actually nonlinear, it has the nonlinear characteristicof relationship #1301 between phase and power. Therefore, compensationdata up table 1001 stores, as compensation data, relationship #1303between amplitude and power symmetrical with relationship #1301 betweenamplitude and power that the actual signal after amplitude has withrespect to relationship #1302 between amplitude and power when amplifier210 has linearity.

FIG. 14 shows a case where, with regard to relationship #1402 betweenamplitude and power, amplifier 210 has linearity, and since amplifier210 is actually nonlinear, it has the nonlinear characteristic ofrelationship #1401 between amplitude and power. Therefore, compensationdata down table 1002 stores, as compensation data, relationship #1403between amplitude and power symmetrical with relationship #1401 betweenamplitude and power that the actual signal after amplitude has withrespect to relationship #1402 between amplitude and power when amplifier210 has linearity.

Similarly, FIG. 15 shows a case where, with regard to relationship #1502between phase and power, amplifier 210 has linearity, and sinceamplifier 210 is actually nonlinear, it has the nonlinear characteristicof relationship #1501 between phase and power. Therefore, compensationdata down table 1002 stores, as compensation data, relationship #1503between amplitude and power symmetrical with relationship #1501 betweenamplitude and power that the actual signal after amplitude has withrespect to relationship #1502 between amplitude and power when amplifier210 has linearity. By this means, compensation data amplitude componentsbecome amplitude components of inverse amplitude to amplitude componentsin amplifier 210 IM waves with respect to amplitude components when theamplifier 210 output signal has a linear characteristic. Also,compensation data amplitude components become amplitude components ofinverse amplitude to amplitude components in amplifier 210 IM waves withrespect to amplitude components when the amplifier 210 output signal hasa linear characteristic.

Next, a description will be given of the operation of transmittingapparatus 900 in a distortion component suppression operation thatsuppresses IM waves #1001, #1002, #1003, and #1004 shown in FIG. 10.

A baseband signal is input to power calculation section 203 and complexmultiplication section 205 as orthogonal data composed of an I componentand a Q component. Power calculation section 203 calculates power fromthe input baseband signals. Then, in compensation data up table 901 andcompensation data down table 902, compensation data is referenced usingmeasured power information and a compensation signal phase component isfound, and also compensation data is referenced using measured powerinformation and a compensation signal amplitude component is found. Atthis time, the relationship between amplitude and power stored bycompensation data up table 901 is that shown in FIG. 13, and therelationship between phase and power stored by compensation data uptable 901 is that shown in FIG. 14. Also, the relationship betweenamplitude and power stored by compensation data down table 902 is thatshown in FIG. 15, and the relationship between phase and power stored bycompensation data down table 902 is that shown in FIG. 16. Tableswitching section 903 then determines whether baseband signal power ison an upward trend or on a downward trend, and outputs the compensationsignal input from compensation data up table 901 to complexmultiplication section 205 if power is on an upward trend, or outputsthe compensation signal output from compensation data down table 902 tocomplex multiplication section 205 if power is on a downward trend. Thecompensation signal is found as a vector from the phase and amplitudecomponents.

Then IM waves #1001, #1002, #1003, and #1004, which are distortioncomponents generated when the baseband signal is amplified by amplifier210, are suppressed by combining the compensation signal and basebandsignal in complex multiplication section 205.

Thus, according to Embodiment 2, in addition to provision of the effectsof above-described Embodiment 1, IM waves can be suppressed usingdifferent compensation data when baseband signal power is on an upwardtrend and when baseband signal power is on a downward trend, enabling IMwaves also to be suppressed with high precision in a case wherelower/upper unbalance occurs whereby power differs betweenlow-frequency-side distortion components and high-frequency-sidedistortion components on the frequency axis generated in a signalamplified by power amplifier 210 due to temperature characteristics, forexample. Also, according to Embodiment 2, compensation table creation isperformed taking account of lower/upper unbalance frequencycharacteristics, enabling a satisfactory suppression effect to beobtained for IM waves generated during input to a multicarrieramplifier.

Embodiment 3

FIG. 16 is a block diagram showing the configuration of a transmittingapparatus 1600 according to Embodiment 3 of the present invention.

As shown in FIG. 16, in transmitting apparatus 1600 according toEmbodiment 3, as compared with transmitting apparatus 200 according toEmbodiment 1 shown in FIG. 2, a compensation data table 1602 is providedinstead of compensation data table 204, and determination section 1601and an IM unbalance compensation computation section 1603 are added.Parts in FIG. 16 identical to those in FIG. 2 are assigned the samecodes as in FIG. 2, and descriptions thereof are omitted.

In FIG. 16, transmitting apparatus 1600 is mainly composed of inputterminal 201, input terminal 202, power calculation section 203, complexmultiplication section 205, DAC 206, DAC 207, oscillator 208, MOD 209,amplifier 210, antenna 211, determination section 1601, compensationdata table 1602, and IM unbalance compensation computation section 1603.

Input terminal 201, input terminal 202, power calculation section 203,complex multiplication section 205, DAC 206, DAC 207, oscillator 208,MOD 209, amplifier 210, determination section 1601, compensation datatable 1602, and IM unbalance compensation computation section 1603 makeup a distortion compensation apparatus 1604. For distortion compensationapparatus 1604 in FIG. 16, a predistortion distortion compensationapparatus configuration is shown, with power calculation section 203,complex multiplication section 205, determination section 1601,compensation data table 1602, and IM unbalance compensation computationsection 1603 forming a predistortion function.

Using at least two items of measured power information in the measuredpower information for each sampling time input from power calculationsection 203, determination section 1601 determines whether measuredpower according to the latest measured power information is rising orfalling in comparison with measured power according to past measuredpower information, and outputs the determination result to IM unbalancecompensation computation section 1603.

Compensation data table 1602 has vector information comprising a datatable of amplifier 210 that has nonlinear characteristics. Thencompensation data table 1602 outputs amplifier 210 nonlinearcharacteristic information to IM unbalance compensation computationsection 1603 based on power information input from power calculationsection 203 and a nonlinearity information table that has vectorinformation. The method of creating the nonlinearity information tablewill be described later herein.

IM unbalance compensation computation section 1603 generates, and storesas a compensation table, a compensation signal based on nonlinearcharacteristic information found at at least two different times inputfrom compensation data table 1602 before a distortion compensationoperation, a coefficient, the result of determination by determinationsection 1601 as to whether measured power is on an upward trend or on adownward trend, and a fixed value when amplifier 210 is assumed to havelinear characteristics—that is, when amplifier 210 performs fixedtransmission operation regardless of input power. IM unbalancecompensation computation section 1603 then references the compensationtable using measured power information input from determination section1601 at the time of a distortion component compensation operation andselects a compensation signal, and outputs the selected compensationsignal to complex multiplication section 205.

Next, the method of creating the nonlinearity information table used bycompensation data table 1602 and the compensation table used by IMunbalance compensation computation section 1603 will be described usingFIG. 17 through FIG. 24. The nonlinearity information table andcompensation table are created in advance prior to a distortioncomponent suppression operation.

A baseband signal is input to power calculation section 203 and complexmultiplication section 205 as orthogonal data composed of an I componentand a Q component. Power calculation section 203 calculates power fromthe input base band signals. Then compensation data table 204 outputsamplifier 210 nonlinear characteristic information to IM unbalancecompensation computation section 1603. At this time, compensation datatable 204 stores the relationship between amplitude and power shown inFIG. 17. Also, compensation data table 204 stores the relationshipbetween phase and power shown in FIG. 18.

Here, the relationship between amplitude and power shown in FIG. 17 isidentical to relationship #1201 between amplitude and power in FIG. 12,and the relationship between phase and power shown in FIG. 18 isidentical to relationship #1301 between amplitude and power in FIG. 13.That is to say, compensation data table 1602 stores the relationshipbetween amplitude and power shown in FIG. 17 and the relationshipbetween phase and power shown in FIG. 18 found by a method identical tothe method up to finding relationship #1201 between amplitude and powerand relationship #1301 between amplitude and power in above-describedEmbodiment 2 as nonlinear characteristic information.

When performing computational processing to show the unbalance IMcharacteristic, IM unbalance compensation computation section 1603 findsthe unbalance IM characteristic based on compensation data at time t-1input from compensation data table 204, compensation data at time tafter the elapse of a predetermined time from time t-1 input fromcompensation data table 204, a coefficient, the result of determinationby determination section 1601 as to whether measured power is on anupward trend or on a downward trend, and a fixed value.

Specifically, the unbalance IM characteristic can be found usingEquation (6) or Equation (7).Real_amp(t)=amp(t)+(amp(t)−amp(t-1))×(Li_amp−amp(t-1))×g   (6)Real_amp(t)=amp(t)−(amp(t)−amp(t-1))×(Li_amp−amp(t-1))×g   (7)where

Real_amp(t): Unbalance IM characteristic at time t

amp(t): Compensation data at time t

amp(t-1): Compensation data at time t-1

Li_amp: Fixed value

g: Coefficient

In this way, IM unbalance compensation computation section 1603 findsthe unbalance IM characteristic shown in FIG. 19 from the amplifier 210nonlinear characteristic shown in FIG. 17, and also finds the unbalanceIM characteristic shown in FIG. 20 from the amplifier 210 nonlinearcharacteristic shown in FIG. 18. As shown in FIG. 19, the relationshipbetween amplitude and power in the unbalance IM characteristic hashysteresis whereby the relationship #1901 between power and amplitudewhen power is on an upward trend and the relationship #1902 betweenpower and amplitude when power is on a downward trend follow differentpaths. Also, as shown in FIG. 20, the relationship between phase andpower in the unbalance IM characteristic has hysteresis whereby therelationship #2001 between power and phase when power is on an upwardtrend and the relationship #2002 between power and phase when power ison a downward trend follow different paths. Relationships between powerand amplitude and between power and phase that have hysteresis of thiskind can be changed by setting coefficient g in Equation (6) andEquation (7) variably.

Next, when IM unbalance compensation computation section 1603 convertsan unbalance IM characteristic to a compensation characteristic andgenerates a compensation signal, IM unbalance compensation computationsection 1603 performs conversion to a compensation characteristic sothat there is symmetry with the unbalance IM characteristic with respectto a fixed value at which amplitude and phase become almost fixed whenamplifier 210 is assumed to have a linear characteristic. Specifically,the compensation characteristic is obtained from Equation (8) using theunbalance IM characteristic and linear characteristic found fromEquation (6) or Equation (7).Compensation characteristic=Li_amp/Real_amp   (8)where

Real_amp: Unbalance IM characteristic

Li_amp: Fixed value

In this way, IM unbalance compensation computation section 1603 convertsthe hysteresis characteristics shown in FIG. 19 and FIG. 20 to thecompensation characteristics shown in FIG. 21 and FIG. 23. FIG. 21 andFIG. 23 are drawings showing the relationship between amplitudecomponents and power in compensation characteristics, and FIG. 22 andFIG. 24 are drawings showing the relationship between phase componentsand power in compensation characteristics.

By converting an unbalance IM characteristic to a compensationcharacteristic, when input power is on an upward trend, relationship#1901 between amplitude and power is converted to a relationship #2101between amplitude and power, and relationship #2001 between phase andpower is converted to a relationship #2201 between phase and power.Also, by converting an unbalance IM characteristic to a compensationcharacteristic, when input power is on a downward trend, relationship#1902 between amplitude and power is converted to a relationship #2102between amplitude and power, and relationship #2002 between phase andpower is converted to a relationship #2202 between phase and power. IMunbalance compensation computation section 1603 stores compensationcharacteristics by storing the relationships between amplitude and powerand the relationships between phase and power shown in FIG. 21 throughFIG. 24 in a compensation table as vector information.

Here, the data table stored by IM unbalance compensation computationsection 1603 is stored as vector information, and the vector informationhas amplitude information and phase information. Therefore, IM unbalancecompensation computation section 1603 has amplitude and phase componentscorresponding to power P input to amplifier 210 as a compensation datatable. That is to say, the relationship between an input signal toamplifier 210 and an output signal from amplifier 210 is expressed asshown in Equation (9).Output signal=amp×input signal   (9)where amp: Amplifier characteristic

Also, amplifier characteristic amp is expressed as shown in Equation(10).amp(P)=A(P)×e^(−jθ(P))   (10)where

A(P): Amplitude component at time t

θ(P): Phase component at time t

P: Power input to amplifier 210

amp(P): Amplifier 210 characteristic

Therefore, the amplifier 210 characteristic can be found as an amplitudecomponent and phase component from Equation (10).

A description will now be given, using FIG. 21 through FIG. 24, of theoperation of transmitting apparatus 1600 in a distortion componentsuppression operation that suppresses IM waves #1001, #1002, #1003, and#1004 when IM waves #1001, #1002, #1003, and #1004 shown in FIG. 10 aregenerated.

If measured power P(t) at time t has risen above measured power P(t-1)at time t-1 according to determination section 1601, IM unbalancecompensation computation section 1603 determines that measured power ison an upward trend, selects A1(t-1) as the amplitude component ofmeasured power P(t-1) at time t-1 and selects A1(t) as the amplitudecomponent of measured power P(t) at time t from FIG. 21, and alsoselects θ1(t-1) as the phase component of measured power P(t-1) at timet-1 and selects θ1(t) as the phase component of measured power P(t) attime t from FIG. 22. IM unbalance compensation computation section 1603then outputs a compensation signal that has compensation characteristicsfor the selected amplitude and phase components. The fixed value here isfound from relationship #2103 between amplitude and power in whichamplitude becomes almost fixed as shown in FIG. 21 and relationship#2203 between phase and power in which phase becomes almost fixed asshown in FIG. 22.

On the other hand, if measured power P(t) at time t has fallen belowmeasured power P(t-1) at time t-1 according to determination section1601, IM unbalance compensation computation section 1603 determines thatmeasured power is on a downward trend, selects A2(t-1) as the amplitudecomponent of measured power P(t-1) at time t-1 and selects A2(t) as theamplitude component of measured power P(t) at time t from FIG. 23, andalso selects θ2(t-1) as the phase component of measured power P(t-1) attime t-1 and selects θ2(t) as the phase component of measured power P(t)at time t from FIG. 24. IM unbalance compensation computation section1603 then outputs a compensation signal that has compensationcharacteristics for the selected amplitude and phase components. Thefixed value here is found from relationship #2303 between amplitude andpower in which amplitude becomes almost fixed as shown in FIG. 23 andrelationship #2403 between phase and power in which phase becomes almostfixed as shown in FIG. 24.

Next, complex multiplication section 205 suppresses IM waves #1001,#1002, #1003, and #1004 comprising distortion components in FIG. 10 bycombining the baseband signal and compensation signal.

Thus, according to Embodiment 3, baseband signal distortion componentsgenerated when a baseband signal is actually amplified are found as afrequency axis series, the found frequency axis series is subjected toIFFT processing and converted to a time axis series, and is held incompensation data table 1602 as amplifier 210 nonlinear characteristicinformation, so that by generating a distortion compensation signalbased on distortion components actually generated in a baseband signal,a compensation signal that takes account of frequency characteristicscan be generated, and distortion components can be suppressed with highprecision. Also, according to Embodiment 3, demodulation processing andso forth is rendered unnecessary and the circuit configuration can bemade small and simple, and furthermore processing can be simplified andspeeded up. Moreover, according to Embodiment 3, IM waves are suppressedafter finding a compensation signal that has different amplitude andphase components when measured power is on an upward trend and whenmeasured power is on a downward trend by correcting amplifier 210nonlinear characteristic information, enabling distortion components ina state of lower/upper unbalance to be suppressed with high precision.

In above Embodiments 1 through 3, IM waves generated when a two-waveinput signal is amplified are suppressed, but this is not a limitation,and the present invention can also be applied to a case where IM wavesgenerated when a single-wave input signal or an input signal of three ormore waves is amplified are suppressed.

As described above, according to the present invention the circuitconfiguration can be made small and simple, processing can be simplifiedand speeded up, and distortion components can be suppressed with highprecision.

This application is based on Japanese Patent Application No. 2002-365448filed on Dec. 17, 2002, the entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention relates to a distortion compensation tablecreation method and distortion compensation method, and is suitable foruse, for example, in a distortion compensation table creation method anddistortion compensation method that eliminate distortion generated whena signal is amplified.

[FIG. 1]

-   103 POWER CALCULATION SECTION-   104 COMPENSATION DATA TABLE-   105 COMPLEX MULTIPLICATION SECTION-   116 COMPENSATION DATA COMPUTATION SECTION-   117 DELAY SECTION    [FIG. 2]-   203 POWER CALCULATION SECTION-   304 COMPENSATION DATA TABLE-   405 COMPLEX MULTIPLICATION SECTION    [FIG. 3]-   START-   ST301 SIGNAL INPUT-   ST302 FUNDAMENTAL AND IM WAVE MEASUREMENT-   ST303 PHASE DIFFERENCE CORRECTION-   ST304 PLOT SIGNALS ON FREQUENCY AXIS-   ST306 FIND TIME t TRANSFER FUNCTION-   ST307 CONVERT TO POWER P TRANSFER FUNCTION-   ST308 END OF PREDETERMINED NUMBER OF TIMES?-   ST309 COMPENSATION TABLE CREATION END    [FIG. 4]-   POWER-   FREQUENCY    [FIG. 5]-   POWER-   FREQUENCY    [FIG. 6]-   POWER-   TIME    [FIG. 7]-   AMPLITUDE-   POWER    [FIG. 8]-   PHASE-   POWER    [FIG. 9]-   203 POWER CALCULATION SECTION-   205 COMPLEX MULTIPLICATION SECTION-   901 COMPENSATION DATA UP TABLE-   902 COMPENSATION DATA DOWN TABLE-   903 TABLE SWITCHING SECTION    [FIG. 10]-   POWER-   FREQUENCY    [FIG. 11]-   POWER-   TIME    [FIG. 12]-   AMPLITUDE-   POWER    [FIG. 13]-   PHASE-   POWER    [FIG. 14]-   AMPLITUDE-   POWER    [FIG. 15]-   PHASE-   POWER    [FIG. 16]-   203 POWER CALCULATION SECTION-   205 COMPLEX MULTIPLICATION SECTION-   1601 DETERMINATION SECTION-   1602 COMPENSATION DATA TABLE-   1603 IM UNBALANCE COMPENSATION COMPUTATION SECTION COEFFICIENT    [FIG. 17]-   AMPLITUDE-   POWER    [FIG. 18]-   PHASE-   POWER    [FIG. 19]-   AMPLITUDE-   POWER    [FIG. 20]-   PHASE-   POWER    [FIG. 21]-   AMPLITUDE-   POWER    [FIG. 22]-   PHASE-   POWER    [FIG. 23]-   AMPLITUDE-   POWER    [FIG. 24]-   PHASE-   POWER

1. A distortion compensation table creation method comprising: a step offinding a distortion component generated in an amplified signal when abaseband signal is amplified by relating frequency to power of saidbaseband signal; a step of converting said distortion component found byrelating frequency to said power so as to be related to time and saidpower; a step of finding an amplitude component and phase component infound said distortion component converted so as to be related to timeand said power for each said power; a step of finding a distortioncompensation signal that has an amplitude component whereby an amplitudecomponent in found said distortion component is an inverse amplitudewith respect to an amplitude component of said amplified signal whensaid distortion component is not present and a phase component whereby aphase component in said distortion component is an inverse phase withrespect to a phase component of said amplified signal when saiddistortion component is not present; and a step of relating found saiddistortion compensation signal and said power and performing storage ina table as compensation signal generation information for selecting saiddistortion compensation signal that suppresses said distortioncomponent.
 2. The distortion compensation table creation methodaccording to claim 1, further comprising: a step of relating said powerto said distortion compensation signal when current said power is risingwith respect to past said power and performing generation as rising-timecompensation signal generation information; a step of relating saidpower to said distortion compensation signal when current said power isfalling with respect to past said power and performing generation asfalling-time compensation signal generation information; and a step ofstoring said rising-time compensation signal generation information andsaid falling-time compensation signal generation information in a tableas said compensation signal generation information.
 3. A distortioncompensation method comprising: a step of finding a distortion componentgenerated in an amplified signal resulting from amplifying a basebandsignal with an amplifier by relating frequency to power of said basebandsignal prior to a distortion component suppression operation; a step ofconverting said distortion component found by relating frequency to saidpower so as to be related to time and said power; a step of finding anamplitude component and phase component in said distortion componentconverted so as to be related to time and said power for each saidpower; a step of finding a distortion compensation signal that has anamplitude component whereby an amplitude component in found saiddistortion component is an inverse amplitude with respect to anamplitude component of said amplified signal when said distortioncomponent is not present and a phase component whereby a phase componentin said distortion component is an inverse phase with respect to a phasecomponent of said amplified signal when said distortion component is notpresent; a step of relating found said distortion compensation signaland said power and performing storage in a table as compensation signalgeneration information for selecting said distortion compensation signalthat suppresses said distortion component; a step of measuring power ofa baseband signal at a time of said distortion component suppressionoperation; a step of selecting said distortion compensation signal byreferencing said compensation signal generation information usinginformation of measured said power; a step of combining said basebandsignal and selected said distortion compensation signal; and a step ofsuppressing with said distortion compensation signal said distortioncomponent generated by amplifying with said amplifier said basebandsignal with which said distortion compensation signal has been combined.4. The distortion compensation method according to claim 3, furthercomprising: a step of relating said power to said distortioncompensation signal when current said power is rising with respect topast said power and performing generation as rising-time compensationsignal generation information; a step of relating said power to saiddistortion compensation signal when current said power is falling withrespect to past said power and performing generation as falling-timecompensation signal generation information; a step of storing saidrising-time compensation signal generation information and saidfalling-time compensation signal generation information in a table assaid compensation signal generation information; a step of selectingsaid distortion compensation signal by referencing said rising-timecompensation signal generation information using information of saidpower when measured said power of said baseband signal is on an upwardtrend, and selecting said distortion compensation signal by referencingsaid falling-time compensation signal generation information usinginformation of said power when measured said power of said basebandsignal is on a downward trend.
 5. A transmitting method comprising: astep of finding a distortion component generated in an amplified signalwhen a base band signal is amplified with an amplifier by relatingfrequency to power of said baseband signal prior to a distortioncomponent suppression operation; a step of converting said distortioncomponent found by relating frequency to said power so as to be relatedto time and said power; a step of finding an amplitude component andphase component in found said distortion component converted so as to berelated to time and said power for each said power; a step of finding adistortion compensation signal that has an amplitude component wherebyan amplitude component in found said distortion component is an inverseamplitude with respect to an amplitude component of said amplifiedsignal when said distortion component is not present and a phasecomponent whereby a phase component in said distortion component is aninverse phase with respect to a phase component of said amplified signalwhen said distortion component is not present; a step of relating foundsaid distortion compensation signal and said power and performingstorage in a table as compensation signal generation information; a stepof measuring transmission power of a baseband signal at a time of saiddistortion component suppression operation; a step of selecting saiddistortion compensation signal by referencing said compensation signalgeneration information using information of measured said basebandsignal power; a step of combining said baseband signal and selected saiddistortion compensation signal; a step of suppressing with saiddistortion compensation signal combined with said baseband signal saiddistortion component generated by amplifying with said amplifier saidbaseband signal with which said distortion compensation signal has beencombined; and a step of transmitting said baseband signal in which saiddistortion component has been suppressed by said distortion compensationsignal.
 6. The transmitting method according to claim 5, furthercomprising: a step of relating said power to said distortioncompensation signal when current said power is rising with respect topast said power and performing generation as rising-time compensationsignal generation information; a step of relating said power to saiddistortion compensation signal when current said power is falling withrespect to past said power and performing generation as falling-timecompensation signal generation information; a step of storing saidrising-time compensation signal generation information and saidfalling-time compensation signal generation information in a table assaid compensation signal generation information; and a step of selectingsaid distortion compensation signal by referencing said rising-timecompensation signal generation information using information of saidpower when measured said power of said baseband signal is on an upwardtrend, and selecting said distortion compensation signal by referencingsaid falling-time compensation signal generation information usinginformation of said power when measured said power of said basebandsignal is on a downward trend.